Method for producing hydrogenous gases

ABSTRACT

Hydrogenous gases are prepared by reacting hydrocarbons with air and/or water at temperatures of from 300 to 1000° C. and a pressure of from 1 to 20 bar in the presence of a catalyst by using a spinel catalyst which comprises at least one element of transition group VIII of the periodic table.

The present invention relates to a process for preparing hydrogenousgases by reacting hydrocarbons with air and/or water at elevatedtemperatures.

EP-A-1 157 968 discloses a process for autothermal steam reforming ofhydrocarbons (preparation of hydrogenous gases) over catalystcompositions which comprise at least one platinum group metal on anoxidic support or on a zeolite.

These catalysts leave something to be desired in their activity andselectivity.

It is an object of the present invention to remedy the abovementioneddisadvantages.

We have found that this object is achieved by a novel and improvedprocess for preparing hydrogenous gases by reacting hydrocarbons oralcohols with water at temperatures of from 300 to 1000° C. and apressure of from 1 to 20 bar in the presence of a catalyst, wherein thecatalyst used is a spinel.

The process according to the invention may be carried out as follows:

In the reaction chamber, the hydrocarbon or the alcohol and water may bereacted at temperatures of from 300 to 1000° C., preferably from 400 to750° C., more preferably from 450 to 700° C., and a pressure of from 1to 20 bar, preferably from 1 to 10 bar, more preferably from 1 to 5 bar,in the presence of a catalyst according to the invention. The reactionmixture of hydrocarbon, air and/or water may be introduced into thereaction chamber without preheating or preferably preheated (for exampleto from 100 to 600° C.). A particular embodiment consists in generatingthe temperature required for preparing hydrogenous gases by partialoxidation of the hydrocarbon using oxygen, preferably air, and only thenadding the reactant stream of water (autothermal steam reforming).

The hydrocarbons may be any desired hydrocarbons, for example crude oil,natural gas, petroleum, diesel, liquefied gas, propane or wastehydrocarbons from chemical processes. These hydrocarbons should besubstantially sulfur-free.

Useful catalysts according to the invention are spinels, preferably anyaluminum spinels, more preferably spinels of the general formulaM_(x)Al₂O₄ where M is Cu or mixtures of Cu with Zn or of Cu with Mg andx is a value from 0.8 to 1.5, preferably from 0.9 to 1.2, morepreferably from 0.95 to 1.1. These spinels generally comprise from 0 to5% by weight, preferably from 0 to 3.5% by weight, of free oxides incrystalline form such as MO (M is, for example, Cu, Zn or Mg) and Al₂O₃.

The catalysts according to the invention show advantageous ageingbehavior, i.e. the catalyst remains active for a long time without beingthermally deactivated.

The catalysts according to the invention comprise copper in oxidic form,calculated as copper oxide CuO, in an amount of from generally 0 to 54%by weight, preferably from 5 to 40% by weight, more preferably from 10to 30% by weight, based on the entire catalyst.

The catalyst according to the invention may comprise further dopants, inparticular Zr, La, Ti, Ce or mixtures thereof in oxidic form. Dopingwith Zr, La or mixtures thereof generally increase the thermal stabilityof the catalysts according to the invention.

The content of doping compounds in the catalyst according to theinvention is generally from 0.01 to 10% by weight, preferably from 0.05to 2% by weight.

The catalyst according to the invention may additionally comprisefurther metallic active components. Such metallic active components arepreferably metals of transition group VIII of the periodic table, morepreferably palladium, platinum, ruthenium or rhodium, in particularrhodium. The content of the metals of transition group VIII in thecatalyst according to the invention is generally from 0.01 to 7.5% byweight, preferably from 0.1 to 2% by weight.

The supported catalysts according to the invention may be in the form ofpellets, honeycombs, rings, spall, solid and hollow extrudates or elsein other geometric shapes, preferably in the form of honeycombstructures.

The catalysts according to the invention may be prepared from oxidicstarting materials or from starting materials which are converted to theoxidic form in the subsequent calcining. They may be prepared by aprocess in which the starting materials comprising Al, Cu and optionallyZn and/or Mg and optionally further additives are mixed in one step,shaped into shaped bodies and optionally treated at temperatures ofabove 500° C.

In one possible embodiment of the process, a mixture of the startingmaterials may be processed to corresponding shaped bodies, for exampleby drying and tableting. These may then, for example, be heated totemperatures of from 500 to 1000° C. for from 0.1 to 10 hours(calcining). Alternatively, water may be added to prepare a deformablemass in a kneader or Mix-Muller which is extruded to give correspondingshaped bodies. The damp shaped bodies may be dried and subsequentlycalcined as described above.

The catalysts according to the invention may be prepared by a processwhich comprises the following steps:

-   -   a) preparation of an oxidic aluminic shaped body which may        optionally comprise Cu and/or further doping metals,    -   b) saturation of the shaped body with soluble metal salts,    -   c) subsequent drying and calcining.

All preparative methods are conceivable which are known to those skilledin the art and may be applied to preparing the catalysts according tothe invention:

For example, a support may be prepared from Cu in the form of Cu(NO₃)₂and/or CuO and an aluminum component. When preparing the support, thestarting materials may be mixed, for example, dry or with the additionof water. Zinc and/or magnesium components may be applied to the supportby a single or repeated saturation. The catalysts according to theinvention are obtained after drying and calcining at temperatures offrom 500 to 1000° C., preferably from 600 to 950° C.

Copper may be used as a mixture of, for example, CuO and Cu(NO₃)₂. Thecatalysts prepared in this manner have a higher mechanical stabilitythan the catalysts prepared only from CuO or only from Cu(NO₃)₂.Preference is further given to optionally using corresponding mixturesof oxides and nitrates of Zn and/or Mg. Instead of oxides and nitrates,pure oxides may also be used when acidic deforming assistants such asformic acid or oxalic acid are additionally added. Particularly whenpreparing the catalysts according to the invention in one step in whichall starting materials are mixed and further processed to give shapedbodies, it is very advantageous to use mixtures of oxides and nitrates.

A useful aluminum component is a mixture of Al₂O₃ and AlOOH. Suitablealuminum components are described in EP-A-652 805.

Furthermore, metals of transition group VIII of the periodic table suchas Pd, Pt, Ru and Rh are applied to the catalysts. These elements may beapplied by known preparation methods, for example by saturation,precipitation, electroless deposition, CVD methods or vapor deposition.Preference is given to applying these noble metals in the form of theirnitrates by a saturation step. After the saturation, the decompositionat temperatures of from 200 to 1000° C. and optional reduction areeffected to give the elemental noble metal. Other known processes mayalso be utilized for applying the noble metals.

The process according to the invention is suitable for obtaininghydrogen in reformer units. The process according to the invention isonly a part of the overall process for obtaining hydrogen for fuelcells. As well as the reforming of hydrocarbons, the overall processalso comprises process stages for removing carbon monoxide from thehydrogenous reformate stream by, for example, one or more water gasshift stages and optionally a selective oxidation. The process stagesfor removing carbon monoxide are disclosed, for example, byWO-A-00/66486, WO-A-00/78669 and WO-A-97/25752.

EXAMPLES Example A

Preparation of the Spinel Catalyst

A mixture of 1978.3 g of Puralox® SCF (from Condea), 1185.9 g of Pural®SB (from Condea), 1942 g of Cu(NO₃)₂×3 H₂O and 47 g of CuO were mulledfor 30 min with 1.5% by weight of formic acid in 400 g of water,extruded to give honeycomb structures (600 cpsi {circumflex over (=)}cells per square inch), dried at 120° C. to constant weight and calcinedat 800° C. for 4 hours. The honeycomb structure was then impregnated inaccordance with its water takeup with Rh(III) nitrate solution (fromHeraeus) so that an Rh content of 2% by weight resulted. Finally, thecatalyst was calcined at 900° C. for 2 hours.

Example B

Preparation of the comparative catalyst in analogy to Catalysis Letters59, (1999) 121 to 127.

In analogy to the preparation described in Catalysis Letters 59 (1999)on page 121 ff, a comparative catalyst was prepared which had thefollowing composition:

-   -   5% by weight of rhodium, 95% by weight of Al₂O₃

Example 1

Autothermal Reforming of Methane

In a reactor, 510 liters of methane and 1210 liters of air were eachheated to 500° C. and passed over 28 ml of the catalyst preparedaccording to example A in order to initially preheat it to the requiredoperating temperature (gas exit temperature from 670 to 710° C.) bycatalytic partial oxidation. 510 liter/h of methane, 1210 liter/h of airand 1020 liter/h of steam were then metered into the reactor instationary operation.

When the catalyst of example A was used, the dry reformate comprised 47%by volume of hydrogen, 5% by volume of carbon monoxide, 13% by volume ofcarbon dioxide and 35% by volume of nitrogen.

When the catalyst of example B was used, the dry reformate comprised 39%by volume of hydrogen, 14% by volume of carbon monoxide, 7% by volume ofcarbon dioxide, 37% by volume of nitrogen and 3% by volume of methane.TABLE Running time [hours] Catalysator 250 500 750 1000 1250 1500 A CH₄100 100 99 99 100 98 conversion [%] A H₂ productivity 48 49 47 47 48 47m² _(H2) at STP/cat * h B CH₄ 93 92 90 88 85 81 conversion [%] B H₂productivity 36 34 34 32 29 25 m² _(H2) at STP/cat * h

1. A process for preparing hydrogenous gases comprising reacting ahydrocarbon with air and/or water at temperatures of from 300 to 1000°C. and a pressure of from 1 to 20 bar in the presence of a catalyst,wherein the catalyst comprises a spinel of the general formulaM_(x)Al₂O₄ where M is Cu or a mixture of Cu with Zn or of Cu with Mg andx is from 0.8 to 1.5 and further comprises up to 5% by weight of freeoxides in crystalline form and at least one element of transition groupVIII of the periodic table.
 2. A process for preparing hydrogenous gasesas claimed in claim 1, wherein the element of transition group VIII ofthe periodic table is rhodium.
 3. A process for preparing hydrogenousgases as claimed in claim 1, wherein the hydrocarbon is an aliphaticand/or aromatic hydrocarbon.
 4. A process for preparing hydrogenousgases as claimed in claim 1, wherein the hydrocarbon is methane.
 5. Aprocess for preparing hydrogenous gases as claimed in claim 1, whereinthe hydrocarbon is natural gas.
 6. A catalyst for preparing hydrogenousgases by reacting hydrocarbons with air and/or water at temperatures offrom 300 to 1000° C. and a pressure of from 1 to 20 bar comprising aspinel of the general formula M_(x)Al₂O₄ where M is Cu or mixtures of Cuwith Zn or Cu with Mg and x is from 0.8 to 1.5 and further comprising upto 5% by weight of free oxides in crystalline form and at least oneelement of transition group VIII of the periodic table.
 7. A process forobtaining hydrogen for fuel cells, comprising producing hydrogen by aprocess as claimed in claim
 1. 8. A process for obtaining hydrogen forfuel cells. comprising producing hydrogen by a process as claimed inclaim 1 and further comprising removing carbon monoxide from hydrogen byat least one upstream process stage for removing carbon monoxide.
 9. Aprocess for preparing hydrogenous gases as claimed in claim 1 whereinthe hydrocarbon is a mixture of hydrocarbons, a petroleum oil, a petrol,a diesel oil or a petroleum oil distillate.